@satishbh Also to add more context to this for others who come across it (using the older version):
The root cause of the error was having an S3 bucket that wasn't public. The plugin then handled the thrown error by the S3 API incorrectly, which was fixed in:
marvin-zhao created this issue in june07/nodebb-plugin-cloudstorage closed Aws s3 don't work #2 0 committed to june07/nodebb-plugin-cloudstorage Fix https://github.com/june07/nodebb-plugin-cloudstorage/issues/2
I found the reason that my bucket wasn't public.